The present invention relates to a transducer for at least one kinematic measurable variable, such as position, speed, or the like, particularly in devices for oil and natural gas production, comprising a first device part which is movable in or through the device, and whose kinematic measurable variable is to be determined, and a second device part which is stationary relative to the first device part. Furthermore, the invention relates to a method and a coding pattern for determining such a kinematic measurable variable.
Such transducers serve, for instance, to determine the position during displacement of the movable device part relative to the stationary device part. With the displacement of the parts relative to one another, the position of a shut-off device, a blow-out preventer, a rotary adjustment device, a valve, a throttle, or the like, is detected and represented at a desired place as positional information. The corresponding devices are used in oil and natural gas production for transportation along transportation pipelines, for changing the transportation capacity of the transportation pipelines, for shutting off the transportation pipelines in case of emergency, for adding chemicals to the transportation lines in a controlled way, or the like. At any rate, exact knowledge of the relative position of movable device part and stationary device part is required.
So far the position has e.g. been determined by assigning a scale to a spindle, a piston, or another movable device part, and by reading the corresponding position of the movable device part relative to the stationary device part from the scale. A further known possibility of determining the position is a potentiometer or linear resistor relative to which a contact is adjusted upon movement of the movable device part, so that the detected resistance is changed.
Finally a further possibility of determining the position is known where slits, or the like, are arranged as coding patterns on a scale at the same linear distance. These are sensed and counted to determine corresponding positions. Instead of a linear arrangement of such slits, a rotary disk is already known with slits arranged at a constant distance in circumferential direction, the slits being also sensed by light detectors, or the like, and then counted.
These known transducers have the disadvantage that in addition to the scanning of the similar and equally spaced subdivisions on the corresponding scale, for instance slits in an encoder disk, the corresponding subdivisions must be summed up in addition to the scanning operation to obtain corresponding information on the position. Furthermore, in the prior-art transducers it is not immediately apparent in which direction the movement actually takes place since it is not readily apparent, for instance, in the case of a straight movement whether the movement is to the left or to the right side. This applies by analogy to a rotating encoder disk in which the rotational direction is not easily detectable by the transducer.
A further drawback is that e.g. upon failure of an electronic means of the transducer the relative position between movable device part and stationary device part can no longer be detected and that a movement up to an end of the possible relative motion range is required to carry out the corresponding position determining operation once again.
U.S. Pat. No. 4,224,603 A discloses a device for locating the position of a moveable component with a binary code and five transducers. According to this document, it is possible to obtain an absolute coded position-location, wherein different displacements are shifted by one bit. The coded bit data is, for example, arranged on some kind of toothed rack and is realized by corresponding activation zones. Different positions or displacements are detected by scanning such coding pattern.
U.S. Pat. No. 5,576,535 A discloses a position detection system with two-bit coding by two types of markings arranged in a pseudo-arbitrary way. The corresponding. markings are provided on a piston rod moveable along a cylinder to which a detector is assigned. Groups of these markings are disposed in such a way that they partially overlap, such that each two successive groups have a different number of markings in common. A scanner unit used for scanning the markings of such a group can be a LED.
EP 0947 805 A is directed to an apparatus for determining the position of a moveable mechanical element. A marking is provided on a piston rod, wherein such markings may comprise code elements as a unique part of a pseudo-random binary sequence. The different code elements are optically readable.
U.S. Pat. No. 5,739,775 A is directed to a digital input and control device used for converting absolute angular or linear mechanical positions to a digital output. A corresponding encoder with conductive and non-conductive rotor segments is scanned by a number of contact elements. The different rotor segments are arranged in a sequence, such that a five-bit output code is realized, which is said to be a gray code sequence.